Molecular regulatory mechanisms which function in the regulation of gene expression in fertilization, development, and growth control will be examined. Protein synthesis is activated at fertilization by a translational control mechanism which activates messenger RNA stored in the egg. Experiments are described to determine the location in the egg of the stored messenger RNA and to elucidate the process of its activation. The cells of early embryos synthesize much more nuclear RNA and messenger RNA than do most other cells. This not only raises the question of the developmental significance of this excessive synthesis, which will be investigated, but also presents an ideal system for studying the metabolism of nuclear and messenger RNA. The mechanisms involved in the selection and transport of messenger RNA from the nucleus, especially in relationship to double-stranded RNA and polyadenylate will be studied. The relationship between translation of a messenger RNA molecule and its transport from the nucleus and its rate of decay will also be examined. When sea urchin larvae are fed they begin to grow and accumulate macromolecules much more rapidly. Protein and DNA synthesis increase substantially. The rate of formation of 28 and 18S ribosomal RNA increases 15 fold over the first 24 hours of feeding. The nutritional factors regulating the stimulus to grow and the molecular mechanisms which function in the acceleration of protein and RNA synthesis will be investigated. The regulatory molecules which are involved in linking the stimulus of the nutritional factors to the molecular mechanisms controlling the activity of the ribosomal genes will be sought.